Systems and methods for on-line pigging and spalling of coker furnace outlets

ABSTRACT

Systems and methods for safe on-line pigging decoking of a coker furnace tubes and which also permits on-line spalling operations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. patent application Ser. No.14/442,713, which is incorporated herein by reference and claimspriority from PCT Patent Application Ser. No. PCT/US14/61845, filed onOct. 22, 2014, which claims priority to U.S. Provisional PatentApplication No. 61/894,087, filed Oct. 22, 2013, which are incorporatedherein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to systems and methods foron-line pigging and spalling of coker furnace outlets. Moreparticularly, the present disclosure relates to systems and methodswhich permit safe pigging of coker furnace tubes and which also permitson-line spalling operations.

BACKGROUND

Coker furnaces typically have four to six tube passes per pair of drums,often configured with two passes per furnace cell. It is not usual forone or more of these to “coke up”-to become constricted due to cokeformation with the furnace cell-during use. Removal of this coke buildupis referred to as “decoking.” Decoking may be necessary annually or moreoften, depending on various factors including design of the coking unitand the nature of the feed.

Historically, for decoking of a furnace cell, the associated (often two)delayed coking drums and the associated furnaces were fully shut down,after which the furnace cell was steam air decoked or offline decoked bymechanically removing the coke with scrapers driven through in the tubesby water (typically referred to as ‘pigging decoking’).

More recently, larger cokers have been built with two or more furnacesoperating in parallel with multiple coke drums and with each furnacehaving multiple tube passes. Safe on-line pigging, that is, piggingdecoking of a furnace cell while the associated delaying coking drumshave continued to operate from input from other furnace cells, has notbeen available because, among other reasons, the piping systemconfiguration must facilitate hazardous energy to be adequatelycontained in each step of operation.

A process referred to as “on-line spalling” has been used to decoke feedin a delayed coking system. In “on-line spalling,” steam is used intypically two of the passes to displace the feed and subsequently toraise the tube metal temperature until the coke ‘spalls off’ the tube.Decoking effluent is then escorted by the steam to mix with the processfurnace effluent from other on-line passes and the combined stream flowsto the coke drum. This beneficially permits decoking without shutting aunit down.

More particularly, on-line spalling occurs when steam is introducedthrough the two furnace coils displacing the process fluid. The steamflow, upon leaving the furnace, rejoins the process fluid furnaceeffluent from the passes which remain in service. Then, the temperatureof the steam and the tube passes which are to be decoked are raised.This temperature increase continues until reaching a temperature far inexcess of normal operations. This may be as high as 1250F depending onthe tube material, thickness. However, piping from furnace outletstypically predates the advent of on-line spalling. As a result, existingpiping and valve systems lack sufficient robustness to permit the highertemperatures of on-line spalling. Attempts to on-line spall with thisexisting equipment may result in failure as the heated piping andcomponents fail pressure containment. Alternatively, that piping may beunusable for generation of a useful pipe stress analysis to determinewhether on-line spalling is possible. For example, use of conventionallow alloy materials, such as 9Cr-1Mo, would result in operation in thematerial's creep range, together with the difficulty in pipe stressanalysis. Thus, for on-line spalling, a higher alloy is typicallyrequired to meet regulatory requirements.

Additionally, on-line pigging decoking of these furnace tubes wouldprovide benefits. While some feeds can be successfully on-line spalledseveral times in a row, because of inorganic deposition or similarreason, the tubes may not return fully to original start-of-runtemperatures. Eventually, these coker furnaces need to be cleaned bymechanical scraper (pigging) decoking. As a result, the need has beenrecognized for both on-line spalling and on-line mechanical scrapercleaning. On-line pigging decoking presents operational and structuralissues, such as safe transitioning among process steps and ensuringcomponents can provide the safety factors needed for on-line pigging.

While both safe on-line pigging of the furnace and on-line spalling ofthe main line may be attractive to the operator of a delayed cokingsystem, safe on-line pigging in conjunction with safe on-line spallingpresents additional issues. In particular, the valves and lines used toprovide a system for safe on-line pigging process, must also be able tosustain the temperatures and pressure line conditions of on-linespalling.

No piping configuration has been identified which permits safe hazardousenergy isolation through all steps for on-line pigging. Nor has a pipingconfiguration been identified which is competent to sustain thetemperatures and pressure line conditions of on-line spalling.

SUMMARY OF THE DISCLOSURE

The present disclosure overcomes one or more deficiencies in the priorart by providing systems and methods which permit safe pigging of cokerfurnace tubes and which also permit on-line spalling operations.

In one embodiment, the present disclosure includes a system for on-linepigging of a tube coil for a furnace in a delayed coking system, whichcomprises: i) a first pressurized steam source in fluid communicationwith the tube coil at a tube coil first end; ii) a main line in fluidcommunication with the tube coil at a tube coil second end and in fluidcommunication with an additional drum input line, the main line having afirst isolation valve between the tube coil second end and theadditional drum input line, the main line having a second isolationvalve between the first isolation valve and the additional drum inputline; iii) a third valve on a second line between a fourth valve and themain line, the fourth valve in fluid communication with the main linevia the second line, the second line in fluid communication with themain line at a point between the tube coil second end and the firstisolation valve; iv) a second pressurized steam source in fluidcommunication with the second line at a point between the third valveand the main line; v) a third pressurized steam source in fluidcommunication with the fourth valve, vi) a fifth valve in fluidcommunication with the second line at a point between the fourth valveand the third valve and in fluid communication with a vent; vii) a thirdline in fluid communication with the main line between the firstisolation valve and the second isolation valve and in fluidcommunication with a sixth valve; viii) a fourth line in fluidcommunication with the sixth valve and a closed blowdown system header;ix) a seventh valve between the closed blowdown system header and thesixth valve; and x) a fifth pressurized steam source in fluidcommunication with an eighth valve, the eighth valve in fluidcommunication with the fourth line between the sixth valve and theseventh valve.

Additional aspects, advantages and embodiments of the disclosure willbecome apparent to those skilled in the art from the followingdescription of the various embodiments and related drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described below with references to theaccompanying drawings in which like elements are referenced with likereference numerals, and in which:

FIG. 1 is a schematic diagram illustrating one embodiment of a systemfor on-line pigging and spalling of coker furnace outlets according tothe present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The subject matter of the present disclosure is described withspecificity, however, the description itself is not intended to limitthe scope of the disclosure. The subject matter thus, might also beembodied in other ways, to include different steps or combinations ofsteps similar to the ones described herein, in conjunction with otherpresent or future technologies. Moreover, although the term “step” maybe used herein to describe different elements of methods employed, theterm should not be interpreted as implying any particular order among orbetween various steps herein disclosed unless otherwise expresslylimited by the description to a particular order. While the presentdisclosure may be applied in the oil and gas industry, it is not limitedthereto and may also be applied in other industries to achieve similarresults.

The following description refers to FIG. 1, which illustrates a systemfor on-line pigging of coker furnace outlets which can also be used foron-line spalling of those coker furnace outlets. On-line pigging permitsa more thorough cleaning of furnace tubes of a delayed coker furnacewhile maintaining operation of the associated delayed coker drumsthrough input from other furnaces.

The disclosure of FIG. 1 illustrates a single pass. In practice, usingthe present disclosure, an operator may pig two passes, to decoke twotube passes 103, in one furnace cell simultaneously, and use only oneon-line pigging manifold to clear and isolate each of the two passes.On-line pigging of tubes associated with a delayed coker furnace in sucha larger system results in less down time and less lost profitopportunity than unit shutdown and off line pigging decoking of the sametubes. The present disclosure provides a system which provides foron-line pigging of those tubes and further provides the flexibility toadditionally perform on-line spalling of those tubes. The presentdisclosure provides a system and method which provides adequate safehazardous energy isolation of the furnace tube passes to be decoked, byproviding double block and purge systems on closed valves. This reducesvalve leakage or failure which could result in partial coking of pipingand valve components, complete blockage by coke buildup in thosecomponents, or even undesirable worker safety events. The presentdisclosure also permits the utilization of steam to displace the processfluid and cool the furnace coils to avoid abrupt shocks which wouldotherwise contribute to tube failure. Thus, the present disclosureadequately and safely isolates furnace passes for on-line pigging, whilemaintaining the flexibility to on-line spall and facilitates asuccessful on-line pigging of the furnace coils.

System Description

Referring now to FIG. 1, a schematic diagram illustrates one embodimentof a system for on-line pigging decoking and on-line spalling decokingof one or more coker furnace tube coils 103 of one or more cokerfurnaces 102 according to the present disclosure. A plurality ofembodiments of the system of the present disclosure may be applied to aplurality of coker furnace tube coils 103. Where the coker furnace 102includes a plurality of coiled tubes 103, each connected the main line108, each of the coiled tubes 103 may be similarly be connected to thepigging unit 104, which includes a launcher and receiver for a pig.

The present disclosure provides a system for on-line pigging of a tubecoil 103 of a furnace 102. The coil 103 can be connected to an openprocess fluid supply 160 or a first pressurized steam supply 148 via afurnace charge line 178, or fully disengaged from both, permittingengagement of the coil 103 at its input to another component. Similarly,the coil 103 is in fluid communication with an input of one or moredelayed coking drums 116, 117 though the main line 108, but may bedisengaged from the main line 108, permitting engagement of the coil 103at its output to another component. The one or more delayed coke drums116, 117 may be in fluid communication with one or more additional cellsof the furnace or other furnaces. As can be appreciated, additional druminput lines 170 from other furnaces or other furnace cells of the samefurnace 102 may be joined to the main line 108 before input to the oneor more coke drums 116, 117. These additional lines may generatepressurization which must be addressed to provide safe operation andprevent coking of the second isolation valve 112 due to leaking of thevalve and heating and cooling of the leaked material.

The main line 108, from the coil 103 to the one or more delayed cokingdrums 116, 117, includes a first isolation valve 110 between the coil103 and the one or more delayed coking drums 116, 117. A secondisolation valve 112 is positioned between the first isolation valve 110and in the input of the one or more delayed coking drums 116, 117. Boththe first isolation valve 110 and the second isolation valve 112 arepreferably directional, and therefore each have a high pressure end. Thehigh pressure end of the first isolation valve 110 is positioned towardthe second isolation valve 112 while the high pressure end of the secondisolation valve 112 is positioned toward the first isolation valve 110.The first isolation valve 110 and the second isolation valve 112 mayeach be a ball valve, such that the high pressure end is thespring-loaded seat end of the valve, as opposed to the fixed seat end ofthe valve.

The main line 108, the first isolation valve 110, and the secondisolation valve 112 are capable of withstanding the several thermaltransients and time at elevated temperature of about 1250° F. during anon-line spalling through these components, and to do so while fullycomplying with all applicable codes and standards, including Recognizedand Generally Accepted Good Engineering Practices. This ensures theyremain undamaged and free of coking to facilitate safe operations insubsequent decokings.

A second line 154 communicates with the main line 108 at a point betweenthe coil 103 and the first isolation valve 110 and provides a pathway toa vent 144 when open. The position of this third line 154 between thecoil 103 and the first isolation valve 110 provides two valves-theisolation valve 110 and the second isolation valve 112-between thefurnace 102 and the one or more delayed coking drums 116, 117, ensuringthe safe environment desired. A third valve 124 is provided on thesecond line 154 between a fourth valve 122 and the main line 108. Whenclosed, the third valve 124 closes the pathway to the vent 144. When thethird valve 124 is open, the fourth valve 122 is in fluid communicationwith the main line 108 via the second line 154. A third pressurizedsteam source 120 is provided and is in fluid communication with thefourth valve 122, such that opening the fourth valve 122 permitspressurized steam to apply blocking force against the third valve 124and a fifth valve 146. The fifth valve 146 is in fluid communicationwith the second line 154 at a point between the fourth valve 122 and thethird valve 124 and in fluid communication with a vent 144. A spectacleblind 152 may be included behind the fifth valve 146 for additionalsafety. A second pressurized steam source 126 is in fluid communicationwith the second line 154 at a point between the third valve 124 and themain line 108, via a flow controller 128, which limits the flow of steamfrom the second pressured steam 126 to the second line 154, and via aninth valve 130, between the flow controller 128 and the second line154. The flow controller 128 may be a flow orifice and may include aflow indicator accessible to the user. Alternatively, the flowcontroller 128 may be controlled by a computer based on user selectedcriteria.

A third line 156 communicates with main line 108 between the firstisolation valve 110 and the second isolation valve 112 and, bycommunicating with a sixth valve 136, provides a pathway to a closedblowdown system header 142. A pressure controller 134 is in fluidcommunication with the third line 156 and is also in fluid communicationwith a fourth pressurized steam source 132. The pressure controller 134may comprise a flow meter and a pressure regulator, where the flow meteris in fluid communication with a flow indicator, and where the pressureregulator is in fluid communication with a pressure indicator. Thepressure controller 134, and its components, may be controlled by acomputer based on user selected criteria. During the step of processfluid or steam from the furnace tubes to the blow down system, thepressure controller 134 permits maintaining a pressure in the third line156 higher than that found in the main line 108 between the secondisolation valve 112 and the pressure downstream of valve 112 to cokedrum. This higher pressure is critical as it prevents oil from otherfurnace passes input from other furnaces or other furnace cells of thesame furnace 102 communicating to the additional drum input lines 170with the one or more delayed coking drums 116, 117 from flowing backwardor upstream through the second isolation valve 112. This providesfurther safety should the second isolation valve 112 be in less thangood condition or if the pressure is sufficiently high to force the ballin the second isolation valve 112 off its fixed seat, by overcoming thespring on the high pressure end. This steam provides a criticaloperational block at this step. Later, this pressure controller 134provides blocking steam for double block and higher pressure purgebetween the second isolation valve 112 and the first isolation valve 110to provide hazardous energy isolation while the coil 103 is beingvented, and thus the fourth pressurized steam source 132 providesoperational and blocking steam, as controlled by the pressure regulator134.

A fourth line 158 is provided which communicates with the sixth valve136 and further provides the pathway to the closed blowdown systemheader 142. A seventh valve 140 is positioned between the closedblowdown system header 142 and the sixth valve 136. A fifth pressurizedsteam source 138 is provided in fluid communication with an eight valve162, which is in fluid communication with the fourth line 158 betweenthe sixth valve 136 and the seventh valve 140. The seventh valve 140 maybe a flow regulating valve, and may be a globe valve. The seventh valve140 assists in maintaining back pressure provided by the pressureregulator 134 and to maintain above the pressure of the process fluiddownstream of the second isolation valve 112 as the furnace coil flow isdiverted to the closed blow down system header 142.

The coil 103 may be connected to the main line 108 by an input flangedswing arm, such as a flanged elbow fitting, 106 in fluid communicationwith the tube coil 103 and to the open process fluid supply 160 by anoutlet swing arm 107 in fluid communication with the tube coil 103. Eachswing arm 106, 107 may be disengaged from the coking system and attachedto a pigging unit 104 to provide a closed loop and pathway for the pig,such that the input swing arm 106 is in fluid communication with anoutput of a pigging unit 104 and the outlet swing arm 107 is in fluidcommunication with an input of the pigging unit 104. Once water isintroduced from a water source 150 to the pigging unit 104, the pig isdriven through the coil 103. This may be repeated as necessary.

Method Description

To adequately and safely isolate furnace passes for on-line pigging,while maintaining the flexibility to on-line spall and facilitating asuccessful on-line pigging of the furnace coils, the present systemmoves from normal operation to a steam-out of the furnace passes beingdecoked to a closed blowdown system, and to depressurize to atmosphere,and on-line pigging, and to a steam-out to blowdown system.

In the method of the present disclosure, pigging a tube coil 103 of oneof a plurality of furnaces 102 or cells of a furnace 102 associated withone or more delayed coking drums 116, 117 may be accomplished whilemaintaining an output from at least the second of the plurality offurnaces or furnace cells to the one or more delayed coking drums 116,117, while maintaining a positive double block and purge in anassociated piping system in each step of the process.

In connection with the present disclosure, the method may be disclosedwith reference to structural elements provided on FIG. 1.

In typical coking operation, before use of the system of the presentdisclosure, the tube coil 103 of a furnace 102 is in fluid communicationwith an open process fluid supply 160 and in fluid communication with aninput of one or more delayed coking drums 116, 117. To prevent the flowof output moving to the vent 144 along a second line 154, located at apoint between the coil 103 and a first isolation valve 110, the thirdvalve 124, provided on the second line 154, is closed. This third valve124, as provided above, is positioned on the second line 154 between afourth valve 122 and the main line 108. The first isolation valve 110 isprovided on the main line 108 between the second isolation valve 112 andthe coil 103.

In the typical coking operation, valves and steam sources must be setand provided to ensure no output from the furnace 102 reaches the vent144. This is accomplished by ensuring a double block and purge settingin that second line 154. A third pressurized steam source 120 suppliespressurized steam to the fourth valve 122, which is in fluidcommunication with the main line 108 via a second line 154 and which isinitially open. A fifth valve 146 is provide in fluid communication withthe second line 154 at a point between the fourth valve 122 and thethird valve 124 and is in fluid communication with a vent 144.Initially, the fourth valve is closed. At this point, the pressurizedsteam supplied from the third pressurized steam source 120 to the thirdvalve 124 and the fifth valve 146 may be characterized as blocking purgesteam. To further prevent any output in the main line 108 from passingto the vent 144, a spectacle blind 152 may be provided between the fifthvalve 146 and the vent 144 and may be closed.

Additionally, pressurized steam is supplied from a second pressurizedsteam source 126 to the second line 154 between the third valve 124 andthe main line 108. A ninth valve 130, initially open, is providedbetween the second pressurized steam source 126 and second line 154.This second pressurized steam source 126 provides spool purging steam tothe second line 154 between the third valve 124 and the main line 108. Aflow controller 128 is provided between the second pressurized steamsource 126 and the ninth valve 130.

Similarly, valves and steam sources must be set and provided to ensureno output from the furnace 102 reaches the closed blowdown system header142. This is accomplished by ensuring a double block and purge settingin a third line 156 and a fourth line 158,. The third line 156 isprovided in fluid communication with the main line 108 between the firstisolation valve 110 and the second isolation valve 112 and in fluidcommunication with a sixth valve 136, initially closed. A pressurecontroller 134 is provided in fluid communication with the third line156 and in fluid communication with a fourth pressurized steam source132. The pressurized steam exiting the pressure controller 134 to thethird line 156 between the main line 108 and the sixth valve 136 isspool purging steam communication with the third line 156 and in fluidcommunication with a fourth pressurized steam source 132. The fourthline 158 is provided in fluid communication with the sixth valve 136 andthe closed blowdown system header 142. A seventh valve 140, initiallyclosed, is provided between the closed blowdown system header 142 andthe sixth valve 136. A fifth pressurized steam source 138 is supplied tothe fourth line 158 between the sixth valve 136 and the seventh valve140 by opening an eighth valve 162. The fifth pressurized steam source138 provides blocking steam purge to the fourth line 158 between thesixth valve 136 and the seventh valve 140.

In the present disclosure, a first step includes terminating a flow ofoutput from the tube coil 103 in a main line 108 to the one or moredelayed coking drums 116, 117 and terminating a process fluid supply 160to the furnace 102, such as by closing a twelfth valve 176 between theprocess fluid supply 160 to the furnace 102. Termination of the flow ofoutput from the tube coil 103 in the main line 108 to the one or moredelayed coking drums 116, 117 may be accomplished by closing the secondisolation valve 112. Thus, the process fluid supply 160 to the furnaceis terminated and the system emptied of heated process fluid, firstlythroughline 108 to the one or more coke drums 116, 117, and then throughthe closed blowdown system header 142. To provide the desired doubleblock and purge safe operation, this includes closing the twelfth valve176, and supplying high pressurized steam from a first pressurized steamsource 148 to the tube coil 103 of the furnace 102, and closing thesecond isolation valve 112 and opening the sixth valve 136.Additionally, the seventh valve 140 is opened sufficiently to maintain apressure on the second isolation valve 112 greater than the pressure onthe opposite side of the second isolation valve 112 to prevent processfluid from other passes on the other side of the valve from leakingthrough as flow is directed to the closed blow down system header 142.The supply of high pressurized steam from the first pressurized steamsource 148 to the tube coil 103 of the furnace 102 continues until allremaining output from the tube coil 103 of the furnace 102 is dispensedto the closed blowdown system header 142. Thus a spool purge is suppliedwhen there is process oil in the main line 108.

Thereafter, the second step provides a steam out to the closed blowdownsystem header 142 in the desired double block and purge safe operation.This includes introducing high pressurized steam from a firstpressurized steam source 148 through the tube coil 103 of the furnace102 and into the main line 108 and displacing the remaining output firstto one or more the coke drums 116, 117, and then, after closing thesecond isolation valve 112, to a closed blowdown system header 142. Atthe same time, the method is maintaining a double block and purge foreach valve not between the furnace 102 and the closed blowdown systemheader 142 to isolate a vent 144 by double blocking the fifth valve 146and the third valve 124, with blocking steam from the third pressurizedsteam source 120. Pressure is maintained upstream of the secondisolation valve 112 higher than the pressure downstream by the steamfrom pressure controller 134 to prevent leakage of the second isolationvalve 112 backward from the direction of the one or more coke drums 116,117 and other furnace passes associated with the additional drum inputline 170. At the same time, the method is maintaining pressure to theclosed blowdown system header 142 when the sixth valve 136 is open, withthe seventh valve 140 is opened sufficiently to allow flow to the blowdown system yet maintaining sufficient pressure on the second isolationvalve 112. To ensure the desired double block and purge safe operation,a high pressurized steam from a second pressurized steam source 126 isprovided through a flow controller 128 to the main line 108 to keep thesecond line 154 clear of process fluid upstream of the third valve 124to avoid coking at all steps when process fluid is in main line 108.

In the third step, the method provides for depressurization of coil 103.Steam is directed through the coil 103 and through the vent 144. Thisincludes terminating the introduction of the high pressurized steam froma first pressurized steam source 148 into the main line 108 andcommunicating the high pressurized steam from the first pressurizedsteam source 148 and the tube coil 103. The first isolation valve 110,the sixth valve 136, and the seventh valve 140 are closed andpressurized steam from a fourth pressurized steam supply 132 ascontrolled by the pressure controller 134 is supplied against the firstisolation valve 110 and the second isolation valve 112. After closingthe first isolation valve 110 and establishing positive blocking steamfrom 134, and the high pressurized steam from the second pressurizedsteam source 126 through a flow controller 128 is closed, then the mainline 108 upstream of first isolation valve 110 is then depressurized toa vent 144. This occurs while maintaining a double block and purge foreach valve between the furnace 102 and the closed blowdown system header142 and between the furnace 102 and the one or more delayed coking drums116, 117, while providing the pressure controller 134 in fluidcommunication with a fourth pressurized steam source 132 and each valveon the main line 108 between the furnace 102 and the one or more delayedcoking drums 116, 117 to maintain blocking steam pressure on the secondisolation valve 112 between the pressure controller 134 and the one ormore delayed coking drums 116, 117. The third valve 124 and the fifthvalve 146 are opened, while the fourth valve 122 is closed. If thespectacle blind 152 was provided and closed, it is now opened. Thus, thesteam from the fourth pressurized steam supply 132 as controlled by thepressure controller 134 performs three functions, serving as blockingsteam between the first isolation valve 110 and the second isolationvalve 112 when those two valves isolate the balance of the system fromthe furnace 102, providing adequate backpressure to keep process oilfrom leaking through the second isolation valve 112 during the step offlow to blowdown, and providing a spool purge to keep the third line 156clear when process fluid is flowing to the one or more coke drums 116,117. The method remains in this step until the coils are sufficientlycleaned by the steam and depressurized to atmosphere.

With the coil 103 at atmosphere pressure, in step four, the coil 103 isprepared for pigging. Provision of the high pressure cleaning steam isterminated and the coil 103 prepared for removal from main line 108 andthe furnace charge line 178. This includes terminating the supply of thehigh pressurized steam from the first pressurized steam source 148 tovent 144, including closing the eleventh valve 174. Here, the steam fromthe first pressurized steam source 148 is used to sweep the coil 103.Disconnecting the tube coil 103 of the furnace 102 from the main line108 and the furnace charge line 178 may be accomplished by unbolting theinlet swing elbow 106 and the outlet swing arm 107. The tube coil 103 ofthe furnace 102 is then connected to a pigging unit 104, such as byconnecting to each flanged swing elbow 106, 107, after the main line 108reaches atmospheric pressure.

In a fifth step, the coil 103 is pigging decoked. The pig, a roundcleaning device, which may have abrasive outer surfaces, is forcedthrough the coil 103, scouring the interior. To do so, a water source150 is then supplied to the pigging unit 104, driving the pig through aswing elbow 106, 107, through the tube coil 103 of the furnace 102 andto the pigging unit 104 via the other swing elbow 107, 106. This may berepeated as many times as necessary.

In the sixth step, the method provides for reconnecting the tube coil103 coil of the furnace 102 to the main line 108 and to the firstpressurized steam source 148, and supplying steam to the tube coil 103of the furnace 102 by opening the eleventh valve 174.

In a seventh step, the coil 103 is then prepared for use. This requiressupplying steam to the tube coil 103 of the furnace 102 and to the vent144 to displace air from the coil. This may be accomplished by closingthe second line 154 to the vent and establishing the desired doubleblock and purge safe operation. The fifth valve 146 and the third valve124 are closed and the fourth valve 122 opened to provide a double blockand purge using steam from the third pressurized steam supply 120. Forsafety purposes, the spectacle blind 152, if used, may also be closed.Thus, the vent 144 is isolated. The first isolation valve 110 and thesixth valve 136 are then opened. The opening of the seventh valve 140 isrestricted to maintain pressure on the second isolation valve 112 untilthe tube coil 103 of the furnace reaches at least about 400° F. and notmore than about 700° F. and until the main line 108 is dry.

In the eighth step, the method provides for reheating the temperature ofthe coil 103. The sixth valve 136 and the seventh valve 140 are openedto the closed blowdown system header 142 and steam is flowed to theclosed blowdown system header 142as the temperature of the furnace 102,or the cell of the furnace 102 off-line, is raised until the tube coil103 of the furnace 102 reaches at least about 400° F. and not more thanabout 700° F. and until the main line 108 is dry. The method providesfor simultaneously maintaining the desired double block and purge foreach valve not between the furnace 102 and the closed blowdown systemheader 142 to isolate a vent 144.

In the ninth step, the method provides, once the dry state is reached,for resuming communication of output to one or more delayed coking drums116, 117 or for on-line spalling. The method first provides forterminating flow to the closed blowdown system header 142 and obtaininga double block and purge for each valve not between the furnace 102 andthe closed blowdown system header 142. The second isolation valve 112 isopened to permit flow to the one or more delayed coking drums 116, 117.The sixth valve 136 and the seventh valve 140 are closed, terminatingflow to the closed blowdown system header 142. The ninth valve 130 isopened to provide spool purge steam.

After the ninth step, on-line spalling through the main line 108, thefirst isolation valve 110, and the second isolation valve 112 may beperformed.

The method then provides for resuming decoking operations. This includesresuming communication from the tube coil 103 in a main line 108 to theone or more delayed coking drums 116, 117 and resuming flow of theprocess fluid supply 160 to the furnace 102 by opening the twelfth valve176. As the first isolation valve 110 and the second isolation valve 112are open, the introduction the process fluid supply 160, a feed stock,to the tube coil 103 of the coke furnace 102 generates the output fromthe coil 103 of the coke furnace 102 which is supplied to the input ofthe one or more delayed coking drums 116, 117 though the main line 108.The temperature of the tube coil 103 in the furnace 102 is then raisedto a standard operating temperature for normal operations, which thenresumes.

While the present disclosure has been described in connection withpresently preferred embodiments, it will be understood by those skilledin the art that it is not intended to limit the disclosure to thoseembodiments. It is therefore, contemplated that various alternativeembodiments and modifications may be made to the disclosed embodimentswithout departing from the spirit and scope of the disclosure defined bythe appended claims and equivalents thereof.

1. A system for on-line pigging of a tube coil for a furnace in adelayed coking system, which comprises: a first pressurized steam sourcein fluid communication with the tube coil at a tube coil first end; amain line in fluid communication with the tube coil at a tube coilsecond end and in fluid communication with an additional drum inputline, the main line having a first isolation valve between the tube coilsecond end and the additional drum input line, the main line having asecond isolation valve between the first isolation valve and theadditional drum input line; a third valve on a second line between afourth valve and the main line, the fourth valve in fluid communicationwith the main line via the second line, the second line in fluidcommunication with the main line at a point between the tube coil secondend and the first isolation valve; a second pressurized steam source influid communication with the second line at a point between the thirdvalve and the main line; a third pressurized steam source in fluidcommunication with the fourth valve, a fifth valve in fluidcommunication with the second line at a point between the fourth valveand the third valve and in fluid communication with a vent; a third linein fluid communication with the main line between the first isolationvalve and the second isolation valve and in fluid communication with asixth valve; a fourth line in fluid communication with the sixth valveand a closed blowdown system header; a seventh valve between the closedblowdown system header and the sixth valve; and a fifth pressurizedsteam source in fluid communication with an eighth valve, the eighthvalve in fluid communication with the fourth line between the sixthvalve and the seventh valve.
 2. The system of claim 1, furthercomprising a ninth valve between the second pressurized steam source andsecond line.
 3. The system of claim 2, further comprising a flowcontroller between the second pressurized steam source and the ninthvalve.
 4. The system of claim 3, further comprising a pressurecontroller between the third line and the fourth pressurized steamsource.
 5. The system of claim 4, wherein the first isolation valve is aball valve and the high pressure end is the spring-loaded seat end ofthe valve and the second isolation valve is a ball valve and the highpressure end is the spring-loaded seat end of the valve.
 6. The systemof claim 4, wherein the flow controller comprises a flow orifice.
 7. Thesystem of claim 4, wherein the seventh valve is a flow regulating valve.8. The system of claim 4, wherein the seventh valve is a globe valve. 9.The system of claim 4, wherein the furnace includes a plurality ofcoils.
 10. The system of claim 4, wherein the pressure controllercomprises a flow meter and a pressure regulator, the flow meter in fluidcommunication with a flow indicator, the pressure regulator in fluidcommunication with a pressure indicator.
 11. The system of claim 4,wherein the flow controller further comprises a flow indicator.
 12. Thesystem of claim 4, wherein the first isolation valve, the secondisolation valve and the main line are capable of withstanding theseveral thermal transients and time at elevated temperature of 1250° F.or so during an on-line spalling.